1. Field of the Invention
The present invention relates to a navigation system.
2. Description of the Related Art
Among conventional navigation systems, there has been a navigation system in which if there is a point unwilling to pass at all costs, such a system searches for a route that detours the point and guides a driver. In searching for routes to the destination and guiding a driver, this navigation system searches for a route to be incurred the lowest search cost to the destination with a detour point being set and a search cost of a route passing the detour point being set high. For instance, cf. JP 09-089580 A (Paragraph Number 0004).
However, because map information used for the navigation system is taken a hierarchical structure classified depending on coverage of a road map, when such a bypass search is applied to a hierarchical search, an attempt to bypass a point away from search points (starting point and destination) results in making a bypass search for map information belonging to the upper layer whose data density is low. As a result, a bigger detour than it needs should be made.